An investigation into hybrid power trains for vehicles with regenerative braking

Imperial Users onl

Advanced propulsion system for hybrid vehicles

A number of hybrid propulsion systems were evaluated for application in several different vehicle sizes. A conceptual design was prepared for the most promising configuration. Various system configurations were parametrically evaluated and compared, design tradeoffs performed, and a conceptual design produced. Fifteen vehicle/propulsion systems concepts were parametrically evaluated to select two systems and one vehicle for detailed design tradeoff studies. A single hybrid propulsion system concept and vehicle (five passenger family sedan)were selected for optimization based on the results of the tradeoff studies. The final propulsion system consists of a 65 kW spark-ignition heat engine, a mechanical continuously variable traction transmission, a 20 kW permanent magnet axial-gap traction motor, a variable frequency inverter, a 386 kg lead-acid improved state-of-the-art battery, and a transaxle. The system was configured with a parallel power path between the heat engine and battery. It has two automatic operational modes: electric mode and heat engine mode. Power is always shared between the heat engine and battery during acceleration periods. In both modes, regenerative braking energy is absorbed by the battery

Advanced Torque Control Strategy for the Maha Hydraulic Hybrid Passenger Vehicle.

An increase in the number of vehicles per capita coupled with stricter emission regulations have made the development of newer and better hybrid vehicle architectures indispensable. Although electric hybrids have more visibility and are now commercially available, hydraulic hybrids, with their higher power densities and cheaper components have been rigorously explored as the alternative. The most commonly used architecture is the series hybrid, which requires a power conversion from the primary source (engine) to the secondary domain. A positive displacement machine (pump) converts the rotational power of the engine into hydraulic power and a second positive displacement machine (motor) converts the hydraulic power back into rotational power to drive the axle or wheel. Having at least one variable displacement unit enables the system of the pump and the motor to form a continuously variable transmission. A series hybrid also includes a secondary power storage device, which in most cases is a high-pressure hydro-pneumatic accumulator. During braking, power flows from the wheels, which drive the second positive displacement machine into the high-pressure accumulator and during acceleration, the power flow is reversed, i.e. power from the high-pressure accumulator is used as an input for the second positive displacement machine which will run in motoring mode and drive the axle or wheel. A mode-switching hydraulic hybrid, which is a combination of a hydrostatic transmission and a series hybrid was recently developed at the Maha Fluid Power Research Center. This thesis focuses on the development of a new torque-based controller for the mode-switching hydraulic hybrid prototype. The aim of this work is to use a uniform control strategy across all vehicle modes instead of multiple controllers for multiple modes. With that in mind, an entirely new system model is developed. This torque-based control strategy, along-with a supervisory controller decides on the usage of the high-pressure accumulator, thereby switching the vehicle from non-hybrid to hybrid mode. A separate engine speed controller is designed to control the engine throttle based on the measured engine speed and a piecewise constant reference engine speed. The model is simulated using standard drive cycles demonstrating the different vehicle modes of operation and the controller action. The architecture of the existing prototype vehicle is modified to implement the new controller and also to prevent leakages when the vehicle is not in use. The data acquisition system is modified to incorporate new installed components. Lastly, baseline measurements taken with the prototype vehicle are compared with the simulations. This improved control strategy allows the vehicle to operate in higher powertrain efficiencies and the uniform nature of the controller results in a better “driver-feel”

Influence of Architecture Design on the Performance and Fuel Efficiency of Hydraulic Hybrid Transmissions

Hydraulic hybrids are a proven and effective alternative to electric hybrids for increasing the fuel efficiency of on-road vehicles. To further the state-of-the-art this work investigates how architecture design influences the performance, fuel efficiency, and controllability of hydraulic hybrid transmissions. To that end a novel neural network based power management controller was proposed and investigated for conventional hydraulic hybrids. This control scheme trained a neural network to generalize the globally optimal, though non-implementable, state trajectories generated by dynamic programming. Once trained the neural network was used for online prediction of a transmission’s optimal state trajectory during untrained cycles forming the basis of an implementable controller. During hardware-in-the-loop (HIL) testing the proposed control strategy improved fuel efficiency by up to 25.5% when compared with baseline approaches. To further improve performance and fuel efficiency a novel transmission architecture termed a Blended Hydraulic Hybrid was proposed and investigated. This novel architecture improves on existing hydraulic hybrids by partially decoupling power transmission from energy storage while simultaneously providing means to recouple the systems when advantageous. Optimal control studies showed the proposed architecture improved fuel efficiency over both baseline mechanical and conventional hydraulic hybrid transmissions. Effective system level and supervisory control schemes were also proposed for the blended hybrid. In order to investigate the concept’s feasibility a blended hybrid transmission was constructed and successfully tested on a HIL transmission dynamometer. Finally to investigate controllability and driver perception an SUV was retrofitted with a blended hybrid transmission. Successful on-road vehicle testing showcased the potential of this novel hybrid architecture as a viable alternative to more conventional electric hybrids in the transportation sector

Component control for the Zero Inertia powertrain

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